This application is a 371 of PCT/GB94/02219 filed Oct. 12, 1994.
This invention relates to gas turbine engines which operate on gas and at least one alternative fuel. A typical application is to a dual fuel gas turbine operating on gas as the primary or main fuel and liquid as the secondary or stand-by fuel.
During the operation of a dual fuel gas turbine on the stand-by fuel, liquid for example, the gas fuel injector passages are open to the hot combustion products of the primary zone. Hence re-circulation of the hot gases within the gas injector passages is inevitable. This problem is exaggerated if the gas passages in question are designed for low calorific value (LBTU) gas fuel and are therefore larger than those designed for natural gas operation.
The ingestion of combustion products may cause damage or blockage of the gas passages. Previous work addressed this problem by purging the gas passages when operating on the stand-by fuel by the use of external pressurised steam or other gases. This method although effective, necessitates the addition of expensive equipment to generate and or supply the purge medium therefore increasing both capital and operating costs.
While the use of compressor air for this purging process has been proposed previously, difficulties involving fuel spilling back (i.e. upstream of the injector nozzle) and flashback have not previously been overcome.